Cutaneous sensory stimuli that are eventually perceived as painful, activate unmyelinated and thinly myelinated afferents that project to the superficial dorsal horn of the spinal cord and innervate nociceptive second-order neurons. The cellular and molecular events that contribute to the central processing of nociceptive information remain obscure. The aim of this proposal is: (i) to determine the functional role of peptide-containing primary sensory neurons in the transmission of somatosensory information, (ii) to examine intracellular events elicited by the interaction of peptides released from sensory neurons with receptors located on neurons in the dorsal horn of the spinal cord. To identify peptide-containing sensory neurons in situ and in cell culture, we have isolated monoclonal antibodies directed against cytoplasmic and surface determinants on functional subsets of sensory neurons. The epitopes recognized by these antibodies have been identified. These antibodies will be used to isolate populations of sensory neurons with defined peptide content to label dorsal root ganglion neurons that have been characterized physiologically in vivo and filled with dyes. The postsynaptic actions of transmitters released from identified sensory neurons will be examined at sensory synapses formed in culture. Substance P receptor interactions will be examined on dorsal horn neurons and on cell lines that express a high density of substance P receptors. Monoclonal antibodies will be generated that interact with substance P receptors. These antibodies will be used to localize substance P receptors on cultured cells and combined with electrophysiological studies to determine the chemosensitivity of spinal cord neurons to substance P. Immunological and physiological studies on the interaction of defined pre- and post-synaptic neurons in cell culture will contribute to a molecular characterization of sensory transmission in the spinal cord. A clearer understanding of sensory transmission in the spinal cord will ultimately be important in the design of better methods of treatment of spinal cord disorders and pain syndromes.